On my ThinkPad T500 I use Linux Mint 6 as my primary OS and a very stripped down version of Windows XP SP3 for games and music production.
My other ThinkPads have various versions of Ubuntu and Linux Mint (570, X20, A21m, T22, A30, G40 and R51)
My audio interface (M-Audio FireWire 410) does not have any Linux drivers so Linux is a no-go for me for quality audio listening. I do have a dual boot with Linux set up. The dual boot has been various versions of Ubuntu or Kubuntu over the past several years. Currently Kubuntu 9.04. The Linux setup is just so I can stay reasonably vaguely familiar with Linux. Mostly Linux just ends up making me frustrated when I try to get things working.